The present invention relates to an apparatus and method for inspecting a connection state of a lead electrode to a bump after the lead electrode is bonded to the bump on an LSI chip. The apparatus and method of the present invention are used in a TAB (tape automated bonding) employed in assembling an LSI chip.
The inner leads (hereinafter referred to as "leads") of an LSI chip are inspected to establish whether or not they are duly connected to the corresponding bumps after the inner lead bonding (ILB). The ILB profile is taken by a CCD camera in the form of image data and the positions of the bump and the lead are determined in the image data. In this way, an out of place of the lead from the right contact position can be detected.
FIG. 1 is a side view of a conventional apparatus for inspecting an LSI device in the assembly process, by which the aforementioned inspection is carried out. A thin flexible lead 3 is formed on a pliable film 4 (sometimes referred to as "TAB tape") and is connected to a bump 2 formed on an LSI chip 1. The chip 1 is immobilized on a stage 6 by means of vacuum adsorption. A holding portion 7 holds the film 4 attached with the lead 3. Above the chip 1, a CCD camera 5 is provided which is used in confirming the positions of the lead and the bump. The CCD camera 5 takes a picture of the connecting portion of the bump to the lead, magnifies, and incorporates it in the form of image data.
The camera 5 takes the image data by placing focus on the upper surface of the bump or of the lead. If the upper bump surface is brought into focus, the upper lead surface automatically comes into focus, since the camera has a predetermined depth of focus. Conversely, if the upper lead surface is brought into focus, the upper bump surface comes into focus. After the image data is taken, the bump and the lead figures are checked to determine whether or not the lead slips from the bump. In this manner, it is possible to detect the out of place of the lead from the right contact position after the ILB.
However, when the lead is just in touch with the bump or when the lead is separated slightly from the bump in an upward direction, causing a connection failure, it is difficult to determine whether or not the lead is duly connected to the bump, from the image data taken by the camera 5.
FIG. 2 represents part of the image data taken by the CCD camera shown in FIG. 1, showing a lead/bump connection state. The longitudinal cross section of the lead 3 (3a, 3b) is a trapezoid, the upper side of which is shorter than the lower side (not shown). When the lead 3 (3a, 3b) is viewed from the above, only the upper surface and taper surfaces are seen, as shown in FIG. 2.
FIG. 3 and FIG. 4 are cross-sectional views taken along line F3--F3 and line F4--F4 of FIG. 2, respectively. In FIG. 3, the lead 3a is duly connected to the bump 2. In FIG. 4, the lead 3b is slightly separated from the bump 2, causing a connection failure. However, such connection failure cannot be detected by the conventional method since both lead 3b and bump 2 are in focus by virtue of the depth of focus inherent in the camera 5, as is evidenced in FIG. 2.